Mingye Ding

Dual-Phase Glass Ceramic: Structure, Dual-Modal Luminescence, and Temperature Sensing Behaviors

Yb(3+)/Er(3+)/Cr(3+) triply doped transparent bulk glass ceramic containing orthorhombic YF3 and cubic Ga2O3 nanocrystals was fabricated by a melt-quenching route to explore its possible application in optical thermometry with high spatial and temperature resolution. It was experimentally observed that Yb(3+)/Er(3+) ions incorporated into the precipitated YF3 nanophase, while Cr(3+) ions partitioned into the crystallized Ga2O3 nanophase after glass crystallization. Importantly, such spatial isolation strategy efficiently suppressed adverse energy transfer among different active ions. As a consequence, intense green anti-Stokes luminescence originated from Er(3+): (2)H11/2,(4)S3/2 → (4)I15/2 transitions, and deep-red Stokes luminescence transitions assigned to Cr(3+): (2)E → (4)A2 radiation were simultaneously realized. Impressively, the intermediate crystal-field environment for Cr(3+) in Ga2O3 made it possible for lifetime-based temperature sensing owing to the competition of radiation transitions from the thermally coupled Cr(3+) (2)E and (4)T2 excited states. In the meantime, the low-phonon-energy environment for Er(3+) in YF3 was beneficial for upconversion fluorescence intensity ratio-based temperature sensing via thermal population between the (2)H11/2 state and (4)S3/2 state. The Boltzmann distribution theory and the two-level kinetic model were adopted to interpret these temperature-dependent luminescence of Er(3+) and Cr(3+), respectively, which gave the highest temperature sensitivities of 0.25% K(-1) at 514 K for Er(3+) and 0.59% K(-1) at 386 K for Cr(3+).

Simultaneous morphology manipulation and upconversion luminescence enhancement of β-NaYF4:Yb3+/Er3+ microcrystals by simply tuning the KF dosage.

A strategy has been adopted for simultaneous morphology manipulation and upconversion luminescence enhancement of β-NaYF4:Yb3+/Er3+ microcrystals by simply tuning the KF dosage. X-ray power diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and photoluminescence spectra (PL) were used to characterize the samples. The influence of molar ratio of KF to Y3+ on the crystal phase and morphology has been systematically investigated and discussed. It is found that the molar ratio of KF to Y3+ can strongly control the morphology of the as-synthesized β-NaYF4 samples because of the different capping effect of F− ions on the different crystal faces. The possible formation mechanism has been proposed on the basis of a series of time-dependent experiments. More importantly, the upconversion luminescence of β-NaYF4:Yb3+/Er3+ was greatly enhanced by increasing the molar ratio of KF to RE3+ (RE = Y, Yb, Er), which is attributed to the distortion of local crystal field symmetry around lanthanide ions through K+ ions doping. This synthetic methodology is expected to provide a new strategy for simultaneous morphology control and remarkable upconversion luminescence enhancement of yttrium fluorides, which may be applicable for other rare earth fluorides.

Tuning into blue and red: europium single-doped nano-glass-ceramics for potential application in photosynthesis

A series of SiO2–Al2O3–NaF–YF3 oxyfluoride glasses and β-YF3 nanocrystals embedded glass ceramics single-doped with europium ions were prepared by high-temperature melt-quenching to explore blue/red luminescent materials for potential application in the photosynthesis of green plants. Both Eu2+ and Eu3+ activators were demonstrated to coexist in this specially designed glass fabricated under ambient atmosphere, which can be well explained based on the optical basicity model of glass and evidenced by emission, excitation and time-resolved spectra. Furthermore, the crystallization strategy has been adopted to convert the precursor glasses into nano-glass-ceramics. As a result, Eu3+ ions partitioned into the precipitated orthorhombic YF3 nanophase, while Eu2+ ions remained in the glass matrix. Such spatial isolation of the different active ions in glass ceramics can effectively suppress adverse energy transfer between Eu2+ and Eu3+, leading to both intense Eu2+ blue and Eu3+ red emissions under ultraviolet light excitation.

Achieving efficient Tb3+ dual-mode luminescence via Gd-sublattice-mediated energy migration in a NaGdF4 core–shell nanoarchitecture

A strategy to realize dual-mode luminescence from identical Tb3+ is provided via Gd-sublattice-mediated energy migration and core–shell engineering techniques. By optimizing the structure of a NaGdF4:Yb/Tm@NaGdF4:Ce/Tb nanoarchitecture, both upconversion and downshifting emissions, originating from 5D4 → 7F6,5,4,3 transitions of Tb3+, are achieved through Yb3+ → Tm3+ → [Gd3+]n → Tb3+ and Ce3+ → [Gd3+]n → Tb3+ energy transfer processes, respectively.

Highly enhanced upconversion luminescence in lanthanide-doped active-core/luminescent-shell/active-shell nanoarchitectures

We reported a new strategy to remarkably improve upconversion luminescence of Ln3+-doped nanoparticles via an active-core/luminescent-shell/active-shell engineering technique. By optimization of the structure of a NaGdF4:Yb@NaYF4:Yb/Er@NaGdF4:Yb sandwich-like nanoarchitecture, a significant enhancement of upconversion emission intensity was realized with the help of the synergistic actions of the suppression of Er-defect energy transfer and the efficient energy transfer from Yb3+ in both active-core and active-shell to Er3+ in the luminescent-shell layer.

Water detection through Nd3+-sensitized photon upconversion in core–shell nanoarchitecture

Herein, a strategy to achieve an 808 nm excitable water probe based on an Nd3+-sensitized core–shell upconversion nanoarchitecture is presented. Specifically, the as-synthesized Yb/Er:NaGdF4@Yb/Nd:NaYF4 active-core@active-shell nanocrystals significantly enhance the Er3+ blue, green and red upconversion emissions with the assistance of spatially confined separation between the Nd3+ sensitizers and Er3+ activators and efficient energy transfer/migration of Nd3+ → Yb3+(shell) → Yb3+(core) → Er3+. To understand the exact mechanisms for water detection, core, core–shell and core–shell–shell samples were prepared and their related water-content dependent upconversion emission and decay behaviors under 980 nm and 808 nm laser excitation systematically investigated. Different to the case of the Yb/Er:NaGdF4 core, the Nd3+-sensitized core–shell product can efficiently avoid excitation attenuation (i.e., absorption of the incident laser) and show two-separated linearity with the logarithm of H2O content at a low water content and high water content intervals, respectively, owing to the combined role of Yb3+ excited state quenching and Er3+ excited state quenching. It is expected that this study could provide insights into the design of upconversion nanoparticle based water sensors.

KF-mediated controlled-synthesis of potassium ytterbium fluorides (doped with Er3+) with phase-dependent upconversion luminescence

Potassium ytterbium fluorides with predictable crystal phases and architectures, such as KYb3F10 nanoplates, KYb2F7 nanoparticles, sub-microplates, sub-microrods, KYbF4 micropolyhedra, K2YbF5 microprisms, microrods and microspheres have been successfully synthesized by simply tuning the molar ratio of KF to Yb3+via a facile and general solution-based route. The influence of the KF dosage on the phase and morphology evolution of potassium ytterbium fluorides has been systematically investigated and discussed. And the mechanism about how the KF/Yb3+ molar ratio influences the anisotropic growth and the phase and morphology evolution was proposed. Taking K2YbF5 microrods as an example, the possible formation mechanism was presented on the basis of XRD patterns and the corresponding SEM images of the intermediate products obtained at different reaction time intervals. Additionally, the upconversion luminescence properties of Er3+ ion (2 mol%)-doped potassium ytterbium fluorides with different crystalline phases and architectures were studied in detail. Importantly, this study may provide a great opportunity for the systematical study of the general synthesis and luminescence properties of potassium ytterbium fluorides with predictable crystal phases and well-defined morphologies, which can offer a reference for the precisely controlled synthesis of other rare earth fluoride compounds.

Tuning the Upconversion Luminescence Lifetimes of KYb2F7:Ho3+ Nanocrystals for Optical Multiplexing

Conventional luminescent color coding is limited by spectral overlap and the interference of background fluorescence, thus restricting the number of distinguishable identities that can be used in practice. Here, we demonstrate the possibility of generating diverse time-domain codes, specially designed for a single emission band, using lanthanide-doped upconversion nanocrystals. Based on the knowledge of concentration quenching, the upconversion luminescence kinetics of KYb2 F7 : Ho(3+) nanocrystals can be precisely controlled by modifying the dopant concentration of Ho(3+) ions, resulting in a tunable emission lifetime from 75.8 to 1944.5 μs, which suggests the practicality of these time-domain codes for optical multiplexing.

Controllable synthesis of lanthanide upconversion nanomaterials through impurity doping

Abstract Generally, electronic, magnetic, and optical properties of many technological nanomaterials are realized by purposely “doping” suitable amounts of external elements into hosts. Recently, it has been reported that impurity doping has significant influence on nucleation/growth of numerous functional nanocrystals, and affords a fundamental approach to modify the crystal phase, particle size, morphology, and electronic configuration of nanomaterials. In this chapter, an overview of the recent progress in doping-induced control of phase structures, sizes, shapes, as well as luminescence properties of upconversion (UC) nanomaterials, has been provided. Additionally, we also elucidate the control of lanthanide (Ln 3+ ) activator distribution in the core–shell structure, which has recently provided new opportunities for scientists to design and tune multicolor emissions of Ln 3+ -doped UC nanoparticles. Finally, we point out the challenges and perspectives of the developing impurity-doping strategy.